Transmit-receive cells



United States Patent() =z,8s`4,=6`0z TRAN C'LLS George David Speake, 'Michaellams lan, and Eric Cottam, Clielinsfd, Ei1gland,-asslgnors to Marconis Wireless Telegraph *'Cmpa'ny Limited, London, Englnd,a British company Application July'9, 1956,'s'eiil No. '593,755 Claims priority, applicationGat Britaih September-2, A"1955 s claims. {crass-'13) This invention relates lto so-ealled transmit-receive cells, hereinafter referred to `by their kcustomary designation of TR cells, ysuchas l'are commonly employed for example in the wave guides of radar system to .protect the receiver portion of the :system against .powerful 'energy direct from the associated transmitter .por-tion.

The invention has Afor 4its -object to providejhig'hly efcient and relatively simple TR cells which can Vbe plugged in to a wave guide and which can be tuned accurately after the completionof vacuum processing and, indeed, even after the cell is'imposition in the guide in which it is to be used. Common present day practice with respect to TR 'cells yis either -to make them broadband or to incorporate them in and as part of resonant cavities, the combination being carefully manufactured to close limits of dimension -so as to be, asit were, ,xed tuned in manufacture. In the -broad -band type of cell the dimensions and shapes of the Yparts have to -be determined to close tolerances before vacuum processing and in manufacture generally and-this-is very costly. Moreover, known broad band cells, though `soon removable and replaceable, are s uch that -removal and lreplacement cannot be effected withoutbreaking the run-of the wave guide and, so far -as the :present applicants are `aware, there is none which can be simply plugged intoa holder in the wave guide (much -as'a valve canbe pliggedtinto -a valve holder) so that removal and replacement can 'be effected without mechanically disturbing the wave guide at all. The known cavity-cell arrangement not :only has the defects of being large, expensive 'and-in :general lrequiring what -may be termed laboratory technique: in manufacture in order that the 'correct tpfredet'erminedoperating frequency may be achieved 'but also the defect fof being utilizable only for its own narrow frequency range.

The main objectf tl'is invention iis to 'avoid 'tlie above defects and difliculties and to provide improved cells which can be simply plugged in to a guide; which can be relatively cheaply manufactured; arid in which "accurate tuning is a matter Aof relatively `sihiple adjustment after vacuum processing.

Another important object'ofthe invention is to provide simple and relatively cheap enoiable TR cells of the type having at least one keep alive electrodejwherein the operatingvoltage of 'the 'keep alive electrode may be accurately predetermined and will remain close to the predetermined value even after considerable periods of ordinary use. This object is achieved by adopting a con- ;truction in which the position of the keep alive electrode s accurately and permanently determined and mainaimed.

According to this invention, a TR cell comprises an anvelope, a pair of tubular main electrodes of taper form :xtendin-g towards one another from opposite ends of :aid envelope, and sealed through said envelope at oppou'te ends thereof, at least one collar member external to said envelope on one of said tubular electrodes, a movable capacity tuning member adjustable in position along Hee l2 the vvlei'rg'th 'of said vc"oll'ar, au`d vacuum tight sealing ineans at Jthe outer ends of said main electrodes.

Preferably there 'is a second vcollar mer'nber external to the envelope on the other main electrode, said `second collar member `being arranged to provide one connection with a wave guide in lwhich the vcell is inserted, the tuning member being adapted to provide the second connection with saidguide when the cell s in position.

Preferably a keep alive electrode is fitted axially within one lof the two main electrodes and its operative end 4is accurately 'positioned with reference to said main electrode by means of ya spacing insulator fixed to said keepalive electrode near said operative end and fitted between said keep-alive electrode and 'the interior of said lmain electrode. The said spacing insulator is preferably Va hollow insulating Acylinder mechanically united with the custornary glass 4tube surrounding 'most ofthe length of the keep-alive electrode and fused on to the said keep-alive electrode.

In the preferred construction the capacity tuning member is vin the 'form of a hollow cylinder with an internal flange on one end, the internal a'nge being internally threaded to engage a screw thread on the collar on one of the main electrodes.

The invention is illustrated in the accompanying drawing which is an elevation, partly in cross-section showing a `preferred form of TR cell in accordance with this invention inserted in position in a wave guide.

Referringto'the drawing the cell thereinshown, which'is a so-'called plug-in Vorre" rnov.';1ble cell,'comprises two "si'rnilar tubular main electodesfoftape'red form each 'of which consists lof ajniet'al sleeve 1 of 4Kovar 'or other material having a coeicien'tof thermal expansion lsuch that it may be `fused in ya satisfactory manner Vto glass, and aconical (or truncated conical) mild steel tip, 2 or 3, brazed thereto. These two main 'electrodes are copper-plated to reduce radio 'frequency losses. The two sleeves are vsealed through opposite ends 'of a `glass envelope 4, the vacuum tightness of which is completed by providing glass end sealing members 5 and 6 over the outer open ends of the sleeves. Through the sealing member 5 is fused a keepalive electrode 7 which is accurately axially located within the tubular electrod'e'along which it runs, by means of an insulating spacer 8. This spacer is constituted by a glass cylinder, which `is fused 'to the keep-alive electrode and is unitary with` a glass insulating tube 9, surrounding the major part of 'thelength of the keep-alive electrode and also fused thereto. The insulator 8 is made accurately to size and itslexternal surface is preferably ground. It tits vaccurately within a 'space provided to receive it inside 'the tip 2 on 'the end of the sleeve 1, and serves to ensure that theope'rating gap around the end of the keepalive electrode will fbe accurate as predetermined and will be 4so maintained in use. Alternatively, and preferably, the glass insulating spacer 8 may be replaced by a ceramic cylinder iitting'o'verthe glass tube 9 and cemented to it. Such a ceramic cylinder need not be externally ground. The--extent'to which the keep-alive electrode extends down the tip is determined, in manufacture, by a jig which is not removed until the said electrode is fixed longitudinally `by fusing to the sealing member 5.

In manufacture the envelope is pumped out through the two main electrodes and before sealing member 6 is sealed oif. Holes 10 are provided in both main electrodes so that the entire interior space of the envelope and of the electrodes is open to the pump during evacuation. After pumping out, gas lling and sealing off, metal collars 11 and 12 are fitted externally of the envelope on to the sleeves 1. The upper collar 11 is externally screwthreaded and on it is screwed a capacity tuning member in the form of a cylinder 13 having an internal ange at one end, internally screw-threaded to screw on to the collar 11. A lock-nut 14 serves to lock the position of the tuning member when adjusted in position for tuning.

The drawing shows the device mounted in a wave guide 15. When so mounted the cell is tuned (by `adjusting the tuning cylinder 13) to resonance, the required inductance for resonance being obtained in manner known per se lby a pair of plates 16 (sometimes called irises) positioned centrally in the guide and having their adjacent edges at a predetermined spacing from the inserted cell and from one another as shown. Contact between the cell and one wall of the guide is made via the collar 12 through a spring contact member 17 in the form of a helical spring `bent round into a circle and fitted into a groove in a member 1S screwed into the guide. As will be seen, the collar 12 is stepped as also is the member 18 so as to govern the degree of insertion of the one into the other and the helical spring 17 and the parts are so dimensioned that when the collar 12 is inserted into the member 18 the spring 17 is deformed or iiattened so that it bites into the collar and into the member 18 to give good electrical contact. At the other end of the cell, contact is made with the tuning cylinder 13 by means of a spring 19 in the form of a ring of spring lingers, the said spring fingers being pressed against the tuning cylinder 13 by the action of a screwed ring 20 arranged as shown to screw into a member 21, and which will obviously, when screwed down, press the spring fingers firmly against the tuning cylinder 13.

It will readily be seen that the construction illustrated, though providing all the advantages of a tuned TR cell of the resonant cavity type, is much simpler constructionally than such a known type of cavity-cell arrangement, consists of only a few relatively easily manufactured parts of robust mechanical construction and can be removed and replaced by a simple plug-in operation without disturbing the run of the wave guide to which it is tted. The cell is easily adjusted for tuning when in position. The construction is also strong against thermal shock since the vacuum-preserving glass seals are all so-called matched seals, i.e. they are seals between glass and metal of the same, or substantially the same coeflicient of thermal expansion. Due to the nature of the construction in which metal parts are brazed to one another (in this connection it may be noted that all the metal parts which have to be xed to one another are lixed by brazing) the cell may be pumped out at high temperature and a pure gas iilling may be used. Furthermore, the position of the keep-alive electrode is accurately determined and maintained so that design performance as regards this electrode will be ensured over a substantial working life.

In practice, the gap between the adjacent ends of the tips 2 and 3 is accurately predetermined in manufacture so that the range of tuning required is not great.

If desired, a second keep-alive electrode similar to and arranged in manner similar to the keep-alive electrode shown may be tted into the other tubular electrode 1, 3 in order to guard against `glow-arc transitions if required.

We claim:

1. A transmit-receive cell including an envelope, a pair of axially disposed sleeves sealed in opposite ends of said envelope, main electrodes of taper form mounted in said 4 sleeves and extending towards one another from opposite ends of said envelope, at least one of said electrodes having an axial bore extending therethrough, glass sealing members extending over the outer open ends of said sleeves, a keep-alive electrode, said keep-alive electrode being tted axially within the axial bore in one of the two main electrodes and having its operative end recessed within said main electrode, first and second collar members, said collar members being mounted externally to the envelope on said sleeves, a waveguide into which said cell is inserted, said iirst collar member forming one connection between said waveguide and one of said main electrodes and said second collar member being arranged to provide another connection with said waveguide, and a movable capacity member, said movable capacity member being adjustable in position along the length of said second collar member and forming' the second connection within said waveguide when the cell is in position.

2. A transmit-receiver cell as set forth in claim 1 wherein said first collar member is connected with said waveguide through a iixedly mounted spring contact member and wherein said second collar member is externally screw-threaded and wherein said movable capacity member is internally screw-threaded and adjustably engages the external screw-threads on said second collar member.

3.A transmit-receive cell as set forth in claim 1 in which said keep-alive electrode is provided with a cylindrical insulator that is insulatingly fitted within the axial bore in said one of said main electrodes and is electrically connected to a terminal extending through the sealed end of one of said sleeves and insulated from the said sleeve.

4. A transmit-receive cell as set forth in claim 1 in which said first collar member is annularly stepped and wherein a coacting annularly stepped support is mounted in one side of the waveguide for receiving said stepped collar member and spring means interposed between said first collar member and said stepped support.

5. A transmit-receive cell as set forth in claim 1 in which said movable capacity member is a hollow tuning cylinder having an internal end flange on one end, said ange being internally screw-threaded and wherein said second collar member is externally screw-threaded to receive the internal screw-threads of said internal end iiange and wherein said waveguide includes a cylindrical litting within which said tuning cylinder is axially adjustable and spring means interposed between said cylindrical fitting and said tuning cylinder for stabilizing the movement of said tuning cylinder into and out of said waveguide.

References Cited in the iile of this patent UNITED STATES PATENTS 2,427,089 Cliiford Sept. 9, 194'/ 2,445,445 Marcum Iuly 20, 1948 2,454,741 McCarthy Nov. 23, 194

2,594,732 Cork Apr. 29, 1952 FOREIGN PATENTS 115,736 Australia Aug. 27, 1942 

